Those arrested are not said to be frontline activists, but writers and bloggers who have discussed reform.
They had already been under a travel ban since February, rights group ALQST says.
The latest arrests come amid concern at the fate of activists already in prison after pushing for women's rights.
Ten women's rights campaigners were put on trial last month following a crackdown beginning in 2018. Three were released last week on bail.
That case has drawn international criticism, with 36 states demanding their release at the UN Human Rights Council.
Who has been arrested?
Saudi authorities have not commented on the latest arrests.
They include at least six men and one woman, according to ALQST. Some reports speak of eight arrests.
Among them is Khadijah al-Harbi, a pregnant feminist writer, and US-Saudi citizen Salah al-Haidar, whose mother was one of the activists recently freed.
Al-Haidar has a family home in Virginia but lives with his wife and child in Saudi Arabia, the Associated Press reports.
The other US-Saudi national arrested was reportedly Badr al-Ibrahim - a writer and doctor.
Scrutiny of Saudi Arabia's human rights record has intensified since the murder of journalist Jamal Khashoggi at the Saudi consulate in Istanbul last October.
Turkish investigators and others have pointed the finger at Crown Prince Mohammed bin Salman, seen as the real power behind the throne, alleging he orchestrated the murder.
But the Saudi authorities deny he was involved and blame a "rogue" operation. Eleven people went on trial in January.
The arrests of activists and writers are seen as an attempt to shut down criticism of the crown prince, who has himself enacted some reforms.
Women's rights in Saudi Arabia have been an enduring focus of international concern, despite some public overtures toward reform from within the kingdom.
The World Economic Forum ranked Saudi Arabia number 141 out of 149 countries around the world for gender equality in 2018.
Saudi women still cannot travel, get married or open a bank account without a male guardian's permission.
Earlier this year, the case of a Saudi woman fleeing her family abroad gained high-profile attention.
Rahaf al-Qunun, 18, barricaded herself in a Bangkok hotel room after immigration officials tried to return her.
The teenager eventually received UN help and has since been granted asylum in Canada.